1. Field of the Invention
The present invention relates to a memory management device which operates to divide a memory into storage blocks so that the stored content is allowed to be erased only in blocks and a facsimile apparatus which is arranged to use the memory management device.
2. Description of the Related Art
Dynamic RAMs (DRAM) and static RAMs (SRAM) are representatively used as memories. The DRAM needs to periodically rewrite data even if it is powered on, while the SRAM operates to hold data only if it is powered on. Both of these memories fail to hold their data without their powers. These memories are required to have a spare battery for backing them up when the power is interrupted. On the other hand, the ROMs are capable of holding data if the power is off, while the ROM often has difficulty in rewriting data. The EPROMs are capable of rewriting data again and again only if ultraviolet rays are applied thereto. Regrettably, however, the EPROM is required to rewrite all the content stored therein. The EEPROM allows a program stored therein to be electrically erased. The program can be erased also in bits. Further, a kind of ROM called as a flash memory has been currently used. The flash memory has a capability of erasing the stored data in blocks, that is, block by block.
As mentioned above, nowadays, many kinds of memories have been commercially made available. Those memories have their merits and demerits. It is now desirous to provide such a memory as keeping the same ease of use as the DRAM or the SRAM and needing no power back-up. The DRAM or the SRAM is capable of easily changing a value of 1 or 0 at the current bit into a value of 0 or 1. On the other hand, the ROM keeps a value of 1 at any bit when it is in the initial state. If some data is written in the ROM, the values of 1 at the bits corresponding to the written data are changed to the values of 0. To return the 0's to the 1's, the ROM is required to do an erasing operation. Hence, unlike the DRAM, the ROM cannot easily change from the 0's to the 1's. For erasing the stored data, the EPROM enables to only erase all the data. The flash memory enables to erase the data only in blocks. Further, like the DRAM, the EEPROM has a capability of erasing the data in bits, that is, bit by bit. The EEPROM, however, is so expensive that it is not made available for general-purpose goods.